Vanadium oxysulfide based cathode materials for rechargeable battery

ABSTRACT

A cathode active composite containing an amorphous composite of vanadium oxide and an inorganic sulfide is provided. In one embodiment the composite contains vanadium pentoxide and phosphorous pentasulfide. An elctrochemical cell and a reversible battery having a cathode containing the cathode active composite are also provided. In one embodiment the battery is a magnesium battery.

BACKGROUND OF THE INVENTION

The present invention is directed to a positive electrode activematerial for a magnesium secondary battery and a magnesium battery witha cathode based on the active material.

Lithium ion batteries have been in commercial use since 1991 and havebeen conventionally used as power sources for portable electronicdevices. The technology associated with the construction and compositionof the lithium ion battery (LIB) has been the subject of investigationand improvement and has matured to an extent where a state of art LIBbattery is reported to have up to 700 Wh/L of energy density. However,even the most advanced LIB technology is not considered to be viable asa power source capable to meet the demands for a commercial electricvehicle (EV) in the future. For example, for a 300 mile range EV to havea power train equivalent to current conventional internal combustionengine vehicles, an EV battery pack having an energy density ofapproximately 2000 WM, is required. As this energy density is close tothe theoretical limit of a lithium ion active material, technologieswhich can offer battery systems of higher energy density are underinvestigation.

Magnesium as a multivalent ion is an attractive alternate electrodematerial to lithium, which can potentially provide very high volumetricenergy density. It has a highly negative standard potential of −2.375Vvs. RHE, a low equivalent weight of 12.15 g/eq and a high melting pointof 649° C. Compared to lithium, it is easy to handle, machine anddispose. Because of its greater relative abundance, it is lower in costas a raw material than lithium and magnesium compounds are generally oflower toxicity than lithium compounds. All of these properties coupledwith magnesium's reduced sensitivity to air and moisture compared tolithium, combine to make magnesium an attractive alternative to lithiumas an anode material.

Production of a battery having an anode based on magnesium requires acathode which can reversibly adsorb and desorb magnesium ions and anelectrolyte system which will efficiently transport magnesium ions.Significant effort in each of these areas is ongoing in many researchorganizations throughout the world and active materials underinvestigation include sulfur in various forms, including elementalsulfur, materials known as Chevrel compounds of formula Mg_(x)Mo₆T_(n),(wherein x is a number from 0 to 4, T is sulfur, selenium or tellurium,and n is 8) and various metal oxides such as MnO₂ (alpha manganesedioxide stabilized by potassium), V₂O₅ and ion stabilized oxide orhollandiates of manganese, titanium or vanadium.

In this regard, cathodic active materials based on vanadium, such asV₂O₅ are extremely promising candidates for the Mg battery cathode,because vanadium is capable of multiple redox reactions betweenV⁵⁺/V⁴⁺/V³⁺ and V metal. Also, V⁵⁺ as a high valence state is quitestable, which means that it is easy to increase the operating voltage.Various research groups have reported efforts directed to utility ofV₂O₅ as a positive electrode active material.

However, vanadium oxide suffers as an active material for insertion anddeinsertion of magnesium ions because of the strong attraction of theMg²⁺ ion for oxygen of the V₂O₅. This attraction leads to sluggishmagnesium ion diffusion and hinders further magnesiation. Thus, lowcapacity and low rates are obtained with V₂O₅ without furthermodification.

Nanocrystalline V₂O₅ provides improved performance, however, it isconventionally known that nanocrystalline materials have low packingdensity and it is difficult to prepare a cathode having a desired highcapacity and yet have sufficiently small dimensions to be useful insmall scale appliance utility. Thus, the volumetric energy density of acell employing nanocrystalline V₂O₅ would not be acceptable forcommercial applications. Moreover, nanocrystalline materials promoteelectrolyte decomposition due to an extremely high surface area of thenanoparticles.

In an ongoing study of cathode active materials of high energy densityfor utility in a magnesium battery the present inventors have studiedmethods to mitigate the strong force of attraction of the magnesium ionfor V₂O₅. Substitution of sulfur for oxygen in the active material inthe form of an oxysulfide compound has been investigated.

Chen et al (U.S. 2013/0171502) describe a hybrid electrode assemblyhaving a central current collector and on one side of the collector, alayer of a lithium ion intercalation material and on the other side alayer of an intercalation-free material such as a graphene. ConventionalLi intercalation materials are listed in paragraphs [0072], [0104] andin claim 12. Included in the list are V₂O₅, V₃O₈, sulfur compounds andany mixture thereof.

Bedjaoui et al. (U.S. 2012/0070588) describe a method to package alithium microbattery. In general description of a microbattery, titaniumoxysulfide is described as a cathode active material.

Zhamu et al. (U.S. 2012/0064409) describes a lithium ion battery havingelectrodes containing nano-graphene-enhanced particulate materials.Conventional cathode active materials described include lithium vanadiumoxide, doped lithium vanadium oxide, metal sulfides and combinationsthereof. Explicit disclosure of a mixture of vanadium pentoxide and asulfide glass forming agent is not made, nor is such a materialsuggested.

Gaillard et al. (U.S. Pat. No. 7,695,531) describe a photolithographicmethod to produce an electrolyte thin film for a lithium microbattery.In general description of a lithium microbattery components, titaniumdisulfide, titanium oxysulfide and vanadium oxide are listed as suitablecathode materials.

Gorchkov et al. (U.S. Pat. No. 6,916,579) describe cathode materials fora lithium ion or lithium metal battery which contains a crystallinevanadium oxide and a chalcogenide of sulfur, selenium or telurium. Amixture of vanadium pentoxide and a sulfide glass forming agent is notsuggested.

Mukherjee et al. (U.S. Pat. No. 5,919,587) describe a composite cathodefor an electrochemical cell which is constructed of an electroactivesulfur polymeric material and a transition metal chalcogenide. Othercomponents such as silica, alumina and silicate may be present.Although, cells based on Group I and Group II metals are describedgenerically, explicit disclosure of a magnesium electrochemical cell isnot made. Vanadium pentoxide is disclosed as an example of thetransition metal chalcogenide, however, a mixture of vanadium pentoxideand a sulfide glass forming agent is not made nor suggested. Phosphorouspentasulfide is not disclosed as a component of the cathode activematerial.

Abraham et al. (U.S. Pat. No. 4,934,922) describe a cathode activematerial being a transition metal oxysulfide, preferably molybdenumoxysulfide. Cells based on Group I and Group II metals are describedgenerically, however, the focus is on lithium cells and explicitdisclosure of a magnesium electrochemical cell is not made.

Ouvrard et al. (Journal of Power Sources, 54 (1995) 246-249) describes avanadium oxysulfide compound of formula V₂O₃S.3H₂O as an intercalationmaterial for lithium ions. A lithium electrochemical cell having apositive electrode containing the vanadium oxysulfide is also described.

Aoyagi et al. (U.S. 2012/0164537) describes a positive electrodematerial for a magnesium battery. The cathodic material is a compositeof vanadium oxide, phosphorous oxide, transition metal oxide and otherelements such as alkali metals, sulfur and halogen. The composite isfused at specific temperatures and times to grow a mixed phase systemcontaining vanadium oxide crystallites in an amorphous phosphorous oxidephase. In Example I-28 a composition based on V₂O₅, P₂O₅, Fe₂O₃ and LiSis described. A mixture of vanadium pentoxide and phosphorouspentasulfide or any sulfide glass forming agent is not disclosed as acomposition of a cathode active material.

Levi et al. (Chem. Mater. 2010, 22, 860-868) reviews the materialsemployed to date as positive electrode compositions and the problemsassociated with each. V₂O₅ aerogels are discussed; however, nowhere is amixture of vanadium pentoxide and a sulfide glass forming agentdisclosed or suggested.

Doe et al. (U.S. 2012/0219856) describe a series of spinel structurecomposites which serve as chalcogenides for a positive electrode forinsertion and deinsertion of magnesium ion. Vanadyl phosphates aredescribed among many others. However, this reference does not discloseor suggest a mixture of vanadium pentoxide and a sulfide glass formingagent.

Amatucci et al. (Journal of the Electrochemical Society, 148(8)A940-A950 (2001)) (listed in Invention Disclosure) describe a study ofnanocrystalline V₂O₅ as an intercalation material for variuos cations.Although this reference indicates improvement in performance isnecessary, disclosure or suggestion of mixture of vanadium pentoxide anda sulfide glass forming agent is not made.

Imamura et al. (Journal of the Electrochemical Society, 150(6) A753-A758(2003)) report the synthesis and characterization of a V₂O₅ carboncomposite as a positive electrode material for a magnesium battery, butdoes not disclose or suggest a mixture of vanadium pentoxide and asulfide glass forming agent as a cathode active material.

Imamura et al. (Solid State Ionics, 161 (2003) 173-180) describes theperformance of a V₂O₅ carbon composite as a positive electrode materialfor insertion and desertion of magnesium ion. Nowhere is a mixture ofvanadium pentoxide and a sulfide glass forming agent disclosed orsuggested.

None of the references cited disclose or suggest a mixture of vanadiumpentoxide and a sulfide glass forming agent as a cathode active materialfor a magnesium battery.

Therefore, an object of the present invention is to provide a V₂O₅ basedcathode active material which meets the requirements of a high energymagnesium battery and overcomes the deficiencies of the V₂O₅ formsconventionally known.

Another object of the present invention is to provide a positiveelectrode based on a modified V₂O₅ based material and a magnesiumbattery containing the positive electrode having significantly improvedenergy density and performance in comparison to known magnesiumelectrochemical devices.

SUMMARY OF THE INVENTION

These and other objects are addressed by the present invention, thefirst embodiment of which includes a cathode active material comprisinga composite of vanadium oxide and an inorganic sulfide compound, whereinthe composite comprises amorphous structure.

In embodiments of the invention the vanadium oxide comprises vanadiumpentoxide (V₂O₅) or consists of V₂O₅.

In another embodiment the inorganic sulfide compound is at least oneselected from the group consisting of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ andGa₂S₃, and the cathode is capable of insertion and release of lithiumions, sodium ions or magnesium ions.

In other embodiments the present invention includes electrochemicalcells containing as a cathode active material, an amorphous composite ofvanadium pentoxide and an inorganic sulfide compound, wherein theinorganic sulfide compound is at least one selected from the groupconsisting of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ and Ga₂S₃.

In another embodiment, the present invention includes a reversiblemagnesium battery comprising: an anode; a cathode; and an electrolyte;wherein the cathode comprises: a current collector; and an activematerial comprising a composite of vanadium oxide and an inorganicsulfide compound, wherein the composite comprises amorphous structure.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The presently preferred embodiments, together with furtheradvantages, will be best understood by reference to the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a magnesium battery according to oneembodiment of the present invention.

FIG. 2 shows a schematic electrochemical test cell according to oneembodiment of the present invention.

FIG. 3 shows a XRD pattern of a V₂O₅—P₂S₅ composite prepared in Example1.

FIG. 4 shows a Raman spectra of a V₂O₅—P₂S₅ composite prepared inExample 1 in comparison to V₂O₅ and to P₂S₅.

FIG. 5 shows an initial linear sweep of voltammogram of V₂O₅—P₂S₅composite prepared in Example 1 in comparison with the state-of-the-artMo₆S₈.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present inventors are conducting a wide scale study and evaluationof materials which may function as cathode active materials for amagnesium secondary battery. The object of this study is to discovercathode active materials which are readily available, safe andcomparatively easy to handle in a production environment and whichprovide a magnesium battery having high capacity and high workingpotential.

Throughout this description all ranges described include all values andsub-ranges therein, unless otherwise specified. Additionally, theindefinite article “a” or “an” carries the meaning of “one or more”throughout the description, unless otherwise specified.

The inventors have surprisingly discovered that amorphous compositionsof vanadium oxide and an inorganic sulfide compound are capable ofinsertion and extraction of metal ions such as lithium, sodium andmagnesium, preferably magnesium. When such amorphous composite isformulated into a cathode production of a magnesium battery having highcapacity and working potential was achieved.

Thus, in the first embodiment, the present invention provides a cathodeactive material, comprising: a composite of vanadium oxide and aninorganic sulfide compound; wherein a structure of the compositecomprises amorphous structure.

The inventors have surprisingly discovered that amorphous vanadium oxidematerials can provide a cathode active material capable of a 3V classredox reaction. In preferred embodiments the vanadium oxide is vanadiumpentoxide (V₂O₅). In the description of the present invention the termsvanadium oxide and vanadium pentoxide may be used interchangeable,unless otherwise specified. Without being constrained by theory, it isbelieved that the amorphous matrix of the composite provides manydefects and distorted spaces for Mg ions. Further, the presence of the Satoms in the matrix “shields” magnesium ions from the strong attractiveforces of the O atoms and allows for enhanced diffusion into and out ofthe matrix. Also, V redox element functions by multiple redox reactionas described above.

Amorphorization of the V₂O₅ may be conducted employing quenching andball milling methods which are conventionally known. Applicants havediscovered that by adding inorganic sulfide compounds as glass formingagents containing at least one of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ andGa₂S₃ to the V₂O₅ during the preparation and by careful monitoring ofthe formation conditions, a substantially amorphous material may beobtained. The actual conditions of time, temperature, compositioncontent, quench method or milling media may vary depending on the agentadded and the content of the components.

In addition, the relative mol % content of V₂O₅ in the compositematerial affects the performance of a magnesium cell containing thematerial as a cathode active ingredient. With a content of about 35% toabout 80% on a mol % basis, greater reversible redox activity may beobtained. Preferably, the content of V₂O₅ may be from 70 to 80 mol %.The inventors have determined however, that the actual most preferredcontent varies according to the actual components of composition. Suchpreferred embodiments may be determined by experimental methodsconventionally known to persons of ordinary skill in the art.

The inorganic sulfide compound may preferably be selected from the groupconsisting of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ and Ga₂S₃. In one highlypreferred embodiment P₂S₅ is used as the inorganic sulfide compound.Mixtures of these compounds may also be employed. In theory anyinorganic sulfide compound that forms a glassy composite with V₂O₅ maybe employed.

According to the present invention, the description “substantiallyamorphous” means that the material when analyzed by XRD does not showany crystalline peaks.

Thus in one embodiment commercially available V₂O₅ having a minimumpurity of 98%, preferably, a minimum purity of 99% and most preferably,a minimum purity of 99.5% may be physically mixed with an inorganicsulfide compound in a selected mole % ratio. The physical mixture maythen be co-comminuted in any conventional milling apparatus such as aball mill until an XRD spectrum of the milled composite mixture isdevoid of peaks associated with a crystalline material.

In another embodiment, the physical mixture of the V₂O₅ and inorganicsulfide compound may be heated in an appropriate furnace or oven andquenched by dropping into water or by pressing between two plates orrollers. The amorphous solid solution obtained may then be pulverized.Although the grain size of the pulverlant material is not limited, in apreferred embodiment, the grain size is 10 μm or less, more preferably 5μm or less and most preferably 1 μm or less.

To prepare the cathode the amorphous V₂O₅-inorganic sulfide compoundcomposite may be mixed with a binder. The binder material is notparticularly limited and any binder recognized by one of skill in theart as suitable may be employed. Suitable binders may includepolyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrenebutadiene rubber (SBR), and polyimide. Polyvinylidene fluoride may beemployed in one preferred embodiment.

In an embodiment of the invention the amorphous V₂O₅-inorganic sulfidecompound composite may be mixed with a carbonaceous material such asgraphite, carbon nanotubes or carbon black.

The amount of binder and carbonaceous material in the cathodecomposition may be no greater than 50% by weight, preferably no greaterthan 30% by weight and more preferably, no greater than 10% by weight.

The cathode according to the present invention may be employed in any ofa lithium battery, sodium battery or magnesium battery. In a preferredembodiment, a reversible magnesium battery having the cathode containingthe amorphous vanadium oxide-inorganic sulfide compound composite isprovided.

The anode of the magnesium battery may be any anode suitable for amagnesium battery, including an anode of magnesium metal or acomposition containing magnesium metal, such as Mg₃Bi₂. The anode activematerial may further include an electrically conductive material and abinder. Examples of electrically conducting materials include carbonparticles, such as carbon black. Example binders include variouspolymers, such as PVDF, PTFE, SBR, and polyimide.

An electrolyte layer may be disposed between the anode and cathode andmay include a separator which helps maintain electrical isolationbetween the positive and negative electrodes. A separator may includefibers, particles, web, porous sheet, or other form of materialconfigured to reduce the risk of physical contact and/or short circuitbetween the electrodes. The separator may be a unitary element, or mayinclude a plurality of discrete spacer elements such as particles orfibers. The electrolyte layer may include a separator infused with anelectrolyte solution. In some examples, for example using a polymerelectrolyte, the separator may be omitted.

The electrolyte layer may include a non-aqueous solvent, such as anorganic solvent, and a salt of the active ion, for example a magnesiumsalt. Magnesium ions provided by the magnesium salt interactelectrolytically with the active material(s). An electrolyte may be anelectrolyte including or otherwise providing magnesium ions, such as anon-aqueous or aprotic electrolyte including a magnesium salt. Theelectrolyte may include an organic solvent. Magnesium ions may bepresent as a salt or complex of magnesium, or as any appropriate form.

An electrolyte may include other compounds, for example additives toenhance ionic conductivity, and may in some examples include acidic orbasic compounds as additives. An electrolyte may be a liquid, gel, orsolid. An electrolyte may be a polymer electrolyte, for exampleincluding a plasticized polymer, and may have a polymer infused with orotherwise including magnesium ions. In some examples, an electrolyte mayinclude a molten salt. In one aspect, the electrolyte may include phenylmagnesium chloride (PhMgCl⁺) aluminum trichloride (AlCl₃ ⁻) intetrahydrofuran (THF) or magnesium perchlorate [Mg(ClO₄)₂] inacetonitrile (ACN). In a preferred embodiment, the electrolyte may beMg(ClO₄)₂ in ACN.

The cathode active material may be present as a sheet, ribbon,particles, or other physical form. An electrode containing the cathodeactive material may be supported by a current collector.

A current collector may include a metal or other electrically conductingsheet on which the electrode is supported. The current collector may beformed of carbon, carbon paper, carbon cloth or a metal or noble metalmesh or foil.

FIG. 1 shows an example of one configuration of a rechargeable magnesiumcell 5. The cell 5 includes a positive electrode 10 including theamorphous V₂O₅-inorganic sulfide compound composite according to theinvention as the cathode active material, an electrolyte layer 12, anegative electrode 14, a cathode current collector 16, a negativeelectrode housing 18, a positive electrode housing 20 including an inertlayer 21, and a sealing gasket 22. The electrolyte layer 16 may includea separator soaked in electrolyte solution, and the positive electrode10 may be supported by the cathode current collector 16. In thisexample, the negative electrode 14 includes an active material ofmagnesium metal.

FIG. 2 shows a schematic diagram of a three electrode cell which may beuseful for evaluation and characterization of the cathode activematerials of the present invention. In FIG. 2 the cell is constructedwith a glass vial having a silicone cap. The reference electrode (R.E.)is a Ag/Ag⁺ electrode consisting of a Ag wire in a reference solution of0.01 M AgNO₃ and 0.1 M tetrabutylammonium phosphate (TBAP) inacetonitrile (ACN). The working electrode (W.E.) is constructed of an 80mesh stainless steel screen upon which a layer of the active material tobe tested is formed. The anode (C.E.) is constructed of a magnesiumfoil. The electrolyte is a 1 M Mg(ClO₄)₂ in ACN. A test cell as shownschematically in FIG. 2 may be useful to conduct cyclic voltammetry,impedance and charge/discharge testing. Such testing may be conducted inan argon atmosphere by placing the test cell in a glove box.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLES

The invented materials were prepared by ball milling of the startingmaterials (V₂O₅ and P₂S₅) under a rotation speed of 370 rpm for 20 h inAr atmosphere. The ZrO₂ balls and pot were used for ball millingsynthesis. After ball milling, the samples were collected under Aratmosphere. The invented sample was mixed with Acetylene black(Denkikagaku Kogyo, HS-100) and PVDF (Kureha, KF9305) inN-methylpyrrolidone (NMP) solution to prepare a homogeneous cathode ink.The obtained ink was cast on an 80 mesh stainless steel and then driedat 120° C. under vacuum.

FIG. 3 shows the XRD pattern of V₂O₅—P₂S₅ material prepared in the ballmilling process. No crystalline peak was observed, which means that theobtained material became amorphous.

FIG. 4 shows the Raman spectra of V₂O₅—P₂S₅ material in comparison withP₂S₅ and V₂O₅. The addition of P₂S₅ provides a different chemicalenvironment from V₂O₅ and P₂S₅. Also, the characteristic peak for Sinclusion was observed at around 400-500 cm⁻¹.

FIG. 5 shows the initial linear sweep voltammograms of V₂O₅—P₂S₅material in comparison with the state-of-the-art Chevrel Mo₆S₈ materialin the conventional based electrolytes (1M Mg(ClO₄)₂ in ACN). Scan ratewas 0.1 mV/sec and the operation temperature was 25° C. The current wascathodically swept and was normalized by the maximum current observed ineach voltammogram. The potential was normalized by the Ag referenceelectrode. The observed working potential of the V₂O₅-inorganic sulfidecompound composite was higher than that of the Chevrel phase. Also,according to our experiments, comparable discharge capacity was obtainedin different Mg battery electrolytes.

In conclusion, the synthesized V₂O₅—P₂S₅ composite prepared in Example 1showed higher working voltage with comparably high discharge capacity,indicating a higher energy density than the state-of-the-art ChevrelMo₆S₈ material (Comparative example 1).

Numerous modifications and variations on the present invention arepossible in light of the above description and examples. It is thereforeto be understood that within the scope of the following Claims, theinvention may be practiced otherwise than as specifically describedherein. Any such embodiments are intended to be within the scope of thepresent invention.

1. A cathode active material, comprising: a composite of vanadium oxideand an inorganic sulfide compound.
 2. The cathode active material ofclaim 1, wherein a structure of the composite comprises amorphousstructure.
 3. The cathode active material of claim 1, wherein thevanadium oxide comprises vanadium pentoxide (V₂O₅).
 4. The cathodeactive material of claim 1, wherein the vanadium oxide consists ofvanadium pentoxide.
 5. The cathode active material of claim 1, whereinthe inorganic sulfide compound is at least one selected from the groupconsisting of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ and Ga₂S₃.
 6. The cathodeactive material of claim 5, wherein the inorganic sulfide is P₂S₅.
 7. Acathode, comprising: a current collector; and the active material ofclaim
 1. 8. The cathode of claim 7, wherein a structure of the compositecomprises amorphous structure.
 9. The cathode of claim 7, wherein thevanadium oxide comprises vanadium pentoxide (V₂O₅).
 10. The cathode ofclaim 7, wherein the vanadium oxide consists of vanadium pentoxide. 11.The cathode of claim 7, wherein the inorganic sulfide compound is atleast one selected from the group consisting of P₂S₅, B₂S₃, SiS₂, GeS₂,Al₂S₃ and Ga₂S₃.
 12. The cathode of claim 11, wherein the inorganicsulfide is P₂S₅.
 13. The cathode of claim 7, wherein the vanadium oxideis vanadium pentoxide (V₂O₅) and the inorganic sulfide compound is P₂S₅.14. The cathode of claim 13, wherein a content of the V₂O₅ is from 70 to80 mol %.
 15. An electrochemical cell comprising: an anode; the cathodeof claim 7; and an electrolyte; wherein the anode and cathode arecapable of absorbing and releasing a metal ion selected from the groupconsisting of a lithium ion, a sodium ion and a magnesium ion.
 16. Amagnesium battery comprising the electrochemical cell of claim
 15. 17.The magnesium battery of claim 16, wherein a structure of the compositecomprises amorphous structure.
 18. The magnesium battery of claim 16,wherein the vanadium oxide comprises vanadium pentoxide (V₂O₅).
 19. Themagnesium battery of claim 16, wherein the vanadium oxide consists ofvanadium pentoxide.
 20. The magnesium battery of claim 16, wherein theinorganic sulfide compound is at least one selected from the groupconsisting of P₂S₅, B₂S₃, SiS₂, GeS₂, Al₂S₃ and Ga₂S₃.
 21. The magnesiumbattery of claim 20, wherein the inorganic sulfide is P₂S₅.
 22. Themagnesium battery of claim 16, wherein the vanadium oxide is vanadiumpentoxide (V₂O₅) and the inorganic sulfide compound is P₂S₅.
 23. Themagnesium battery of claim 22, wherein a content of the V₂O₅ is from 70to 80 mol %.